Safety lighting circuit



' March Z, 1937. A, KAMM 2,072,337

SAFETY LIGHTING CIRCUIT Filed fla 5, 1936 P0551 TA/QMM enema-Mir. z, 1931,

UNITED .srAres PATENT OFFICE SAFE LIGHTING Robert A. Kamnn llartlord, Com, asslgnor, by

direct and mesne ents, to The Noi'ade Electric Corporation, Hartford, Conn, a corporation of Connecticut A Application May 5, 1930, Serial Nev-1,991

ifllaims. (c1.1':1-9i) This invention mates to a saigty electric light- 1o illumination embodying several lamps and where-- 'in each lamp was bridged by a resistance coil. Whenever a lamp burned out, the circuit was maintained to other lamps through the bridgin resistance However, these resistances have not '15 only taken an additional amount of c rent, but they have passed more and more current'as the lamps successively burned out, thus resulting inabnormal heating of the circuit and presenting a serious flre hazard to the highly inflammable 20 Christmas tree. Hence, with prior circuits of this type, it will be appreciated that a considerable current would pass through the circuit even when all thelamps burned out. At this time, it

would not be evident that .the circuit'was con nected,' and the hazard wouldbe at amaxi- I mum.

It is, thereiorathe primary object of the pres- L ent invention to provide an electrical lighting equipment such as employed for a decorative, ef- 30 feet on a Christmas tree and embodying safety features which prevent excessive overheating of the circuit. v

It is a further object of this invention to provide a series circuitwherein one or more lamps .35 in the circuit may burn out without breaking the circuit or causing an excemive current flow therethrough.

It is a further object to employ a series circuit including a master control lamp which 40 serves to break the circuit when the current flow therethrough becomes excessive to the other lamps. I i V I With these and other objects in view, my invention resides in the unique construction and the combination of members hereinafter fully described, illustrated in the accompany drawing,-

and referred to in the claims appended hereto; it being understood, of course, that various 50 changes in the general form, proportion, and size, as well as other minor details of construction lying within the scope of the claims, may be resorted to without departing irorn the spirit of the invention or sacrificing any of its advantages. In the accompanying drawing illustrating one embodiment ofm y invention and wherein like parts are indicated by like numerals:

Figure 1 is a diagrammatic illustration of my safety circuit showing the various lamps in series ,connection;

- l Fig. 2 is asectional view through a socket of one of ,the lamps in the series and illustrating the shunt connected therewith;

Fig. 3 is an enlarged sectional view through the shunt member; and Fig. 4 illustrates a modified construction where-- in the shunt is supported in a separate container. In accordance with the present invention, I

- have provided an electrical circuit including. a, wire lead I 0 in the form of a loop and respectively connected at its opposite ends t6 the terminals H and I2 of a connector plug it arranged for detachable connection with a suitable sourceof current supply. Lead wire I 0 is broken in several places, and a plurality of sockets carrying elec-- tric lamps are connected therebetween to form a completed series circuit. In the present instance, ten sockets and lamps have been shown, but it will 1 be appreciated that any number may be em;' ployed to accomplish the purposes of the present invention. One of the sockets, designated herein by the letter A, comprises a master socket arranged to support a master control lamp l5.v The other sockets and lamps in the circuit, herein designated bythe respective letters C and D, are so of duplicate form and so arrange that in the event one of the lamps D burns o t, the other lamps in, the circuit will continue to remain lighted with substantially the same luminosity.

Each of the sockets C is provided with an insulating casing I6 substantially cup shaped and having an inner cavity I! open at its upper end" and terminating at its lower end ina wall l8- provided with an aperture l9 through which the connection wires may pass. The upper end of aperture l1 terminates in a counterbored portion 2| within which any well-known type 0! socket may be spring pressed to removably maintain it within casing l6. In the present instance, this socket is shown as a screw threaded receptacle 22 having a lower insulating portion supporting a center terminal 23 so that a standard type of.

incandescent electric lamp may be screwed therein. Leads 24 and 25- respectively soldered to receptacle 22 and terminal 23 are connected across each break in wire l0 to'complete the circuit through each electric lamp. g- Cavity 11, is preferably, of suiiicient depth to also include a shunt member. 26 arrangedto complete the circuit in the event that" lamp n 2 becomes burned out. While diiierent types of shunts may be used in the circuit, there is herein illustrated the shunt disclosed and claimed in my copendihg application, Serial No. 104,641

5 filed October 8,1936. As shown inFig. 3, shunt familiar type of quick detachable clip or other,

connection, would accomplish the same purpose I 5 and lies. within the scope of the present invention. Plugs 28, as herein shown, are frictionally received within tube 21, but may be secured therein by other means if desired.

The cavity b tween the inner ends of plugs 28 is partially ed with minute metallic clips which tend to oxidize. In the present instance. I preferably employ chips of aluminum, but it will be appreciated that otheroxidizable metals such as. brass, iron, etc, may be employed for the same purpose. Due to the contact of these aluminum chips with the air, each .chip becomes coated with a thin layer'of oxide which increasesthe resistance to electrical flow through the chips, normally preventing any appreciable flow of electrical current between the plugs 28 and causing it to take the easier path through a lamp. The cavity between the plugs, as indicated in Fig. 3, is preferably a little more than half filled with these loose aluminum chips so that the chips will not become compacted but will be free to oxidize under influence of the air in said cavity.

In the eventthat a lamp D burns out, the cur-'- rent flow in the .circuit will not become broken 40 but will pass through the metallic chips. Hence, it'will be appreciated that several lamps-in the circuitfmay become burned out without breaksing the circuit, and if these lamps comprise part of a series circuit such as is commonly used in lighting a Christmas tree, it will immediately be evident-which lamps are burned out, and they I may be quickly replaced with a'minimum of, effort, thus obviating the usual procedureofremoving and testing'each lamp in turn to find 5 which one is" burned out. ,When a'burned out lamp has been replaced, it is only necessary to lightly tap the socket and upset the position of the aluminum chips whereupon other portions of their oxide coatings will contact and current igniting an easily inflammable Christmas tree resent invention with disastrous results. Th has been devised with though 4:0 overcoming the inherent disadvantages of these prior types of shunted series circuits and-consequently includes the master lamp B located in. socket A. This master lamp is removably positioned in a standamassv ard type of socket it connected by means of leads '30 and 31 in series relation to loop l0 so that whenever the current flow thro'ugh the lamps and shunts forming the rest of the circuit bevcomes excessive due to .the fact that many of the lamps D have become burned out, this excessive current flow will serve to burn out the filament-oflamp B and break the circuit. Hence, it'will be appreciated that lamp B not only serves the same decorative effect as lamps D and may be interchangeable therewith, but also provides a safety feature for the circuit which prevents fire hazard or excessive current flow through shunts 26 which would tend to injure them. In

the present instance, the individual resistances of shunts 26 are preferably so chosen that mas ter lamp B will burn out and break the circuit when approximately half of the remaining lampshave became burned out, thereby providing an 1 ample factor of safety and obviating the hazard of overheating and overloading the circuit.

Fig. 4 illustrates a modified construction of my invention wherein the shunt member 26 need not be supported within a socket C but is conrality of electric lamps in series connection, one

of said lamps serving as a master control to prevent overloading of the circuit, and means associated with each of the other lamps automatically providing a predetermined resistance across 4 each of said other lamps when they become burned out.

2. In a safety lighting circuit, a plurality of electric lamps in'series connection, one of said lamps comprising a master control lamp and limi'ting the current flow through the circuit, and shunt members respectively connected across the terminals of each of the other lamps, said shunts normally resisting current flow therethrough and being arranged to maintain the circuit closed when one or more of the lamps associated there-- with becomes burned out.

- M 3. A safety lighting circuit comprising a plulamps each having a shuntmember connected therewith arranged to maintain the circuit closed as said other lamps become successively burned out.

tion, a plurality. of electric lamps connected in series, a load carrying resistance connected across the leads of each lamp and having a pre-R. determined increased resistance relative to the lamp, and a master control lamp connected in series with said first lampsand having ailla ment resistanceequal to the combined resistances oi, a predetermined number of said lead carryingresistances, whereby upon the burning out of a number of said first lamps said master 4.- In a sa fety lighting circuit, and in eombina--- control lamp will burn out and break the cir- ROBERT 1. 1mm. 

